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Molecular Crystallization Controlled by pH Regulates Mesoscopic Membrane Morphology.
MedLine Citation:
PMID:  23185994     Owner:  NLM     Status:  Publisher    
Co-assembled molecular structures are known to exhibit a large variety of geometries and morphologies. A grand challenge of self-assembly design is to find techniques to control the crystal symmetries and overall morphologies of multicomponent systems. By mixing +3 and -1 ionic amphiphiles we assemble crystalline ionic bilayers in a large variety of geometries that resemble polyhedral cellular crystalline shells and archaea wall envelopes. We combine TEM with SAXS and WAXS to characterize the co-assembled structures from the mesoscopic to nanometer scale. The degree of ionization of the amphiphiles and their intermolecular electrostatic interactions are controlled by varying pH. At low and high pH values, we observe closed, faceted vesicles with two-dimensional hexagonal molecular arrangements and at intermediate pH we observe ribbons with rectangular-C packing. Furthermore, as pH increases we observe interdigitation of the bilayer leaflets. Accurate atomistic molecular dynamics simulations explain the pH-dependent bilayer thickness changes, and also reveal bilayers of hexagonally packed tails at low pH, where only a small fraction of anionic headgroups is charged. Coarse-grained simulations show that the mesoscale geometries at low pH are faceted vesicles where liquid-like edges separate flat crystalline domains. Our simulations indicate that the curved-to-polyhedral shape transition can be controlled by tuning the tail density in regions where sharp bends can form the polyhedral edges. In particular the pH acts to control the overall morphology of the ionic bilayers by changing the local crystalline order of the amphiphile tails.
Cheuk-Yui Leung; Liam C Palmer; Bao Fu Qiao; Sumit Kewalramani; Rastko Sknepnek; Christina J Newcomb; Megan A Greenfield; Graziano Vernizzi; Samuel I Stupp; Michael J Bedzyk; Monica Olvera de la Cruz
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-11-27
Journal Detail:
Title:  ACS nano     Volume:  -     ISSN:  1936-086X     ISO Abbreviation:  ACS Nano     Publication Date:  2012 Nov 
Date Detail:
Created Date:  2012-11-28     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101313589     Medline TA:  ACS Nano     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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